1. Field of the Invention
The present invention relates generally to communications networks. More particularly, the present invention relates to a method and apparatus for delivering short message service (SMS) messages to a subscriber, particularly in a wireless communication network including a plurality of short message service centers (SMSC).
2. Background of Related Art
In order to accommodate a society which is becoming increasingly mobile, and to meet the ever-increasing need for communications, the telecommunication industry in particular has been providing wireless communication services.
The wireless communication services traditionally included voice cellular phone and paging services in which a user can make a telephone call or send/receive a page including a numeric message indicating a telephone number over a wireless network. More recently, paging services have been expanded to offer alphanumeric paging, which allows a short text based message to be sent to and displayed at a handheld pager.
However, voice cellular telephone and the paging services each require an intended subscriber to be on-line or active to receive a telephone call or transmitted paging message. In other words, these services do not typically offer the capability of storing the messages for a temporarily unavailable subscriber.
In the early 1990s, as a result of the growing popularity of digital wireless technology, a standard for digital wireless networks was introduced in Europe. That standard, now known as the global standard for mobiles (GSM), included a service called short messaging service (SMS). An SMS allows transmission of short messages, typically up to 160 characters, to and from communication devices, e.g., cellular telephone handsets, telephones or computers with appropriate modems. In North America, the SMS is currently implemented on digital wireless/mobile networks, such as a PCS network based on the GSM standard, code division multiple access (CDMA) and/or time division multiple access (TDMA) methods. Short message services are gaining in popularity, particularly in the United States.
Short message services are advantageous over text based paging services because of the capability of bi-directional communication. Such bi-directional communication allows, for example, notification to the originating device of the success or failure of the short message delivery.
Moreover, each SMS network typically includes a short message service center (SMSC) which acts as a store-and-forward mechanism providing guaranteed delivery of short messages to a subscriber, even if the subscriber is inactive when the message was transmitted, by delivering the short messages once the subscriber becomes active. Delivery of all short messages is guaranteed regardless of whether or not the intended subscriber is "on-line" because the transmitted short message is stored within the one SMSC assigned to each intended subscriber, and delivered to the intended subscriber from their assigned SMSC when the subscriber becomes available.
A variety of services have been introduced using SMS networks including, for example, integrated electronic mail and fax, integrated paging, interactive banking, and information services such as stock quotes and airline schedule delivery.
Unfortunately, conventional SMS networks have been somewhat limited in their utility because they are based on the concept of a single SMSC assigned to service any one particular subscriber. Thus, a particular subscriber is limited to a single message delivery channel between itself and the SMSC that services it. Moreover, because of the singular SMSC architecture of conventional SMS networks, it is difficult if not impossible to upgrade or perform maintenance on an SMS network without affecting and/or suspending the short message service at least with respect to the subscribers assigned to that SMSC.
In operation, an SMSC receives a short message from any source intended to be delivered to a particular subscriber. When the intended subscriber is not available because, for example, it is turned off or is outside of the service area of the SMS network, the attempt to deliver the short message at that time will fail. In this case, the short message will be retained in the SMSC assigned to that intended subscriber for a later delivery attempt. Thereafter, when the subscriber finally becomes available, e.g., is turned on or has moved into the service area of the SMS network, the relevant portions of the network (e.g., the mobile servicing center (MSC) and the home location register (HLR)) notify the SMSC to initiate delivery of the stored (i.e., previously failed) short messages.
A conventional SMS network notifies only the servicing SMSC that an intended subscriber can again receive short messages. Thus conventional SMS networks do not have more than one SMSC assigned to any one particular subscriber.
In order to fully appreciate the above shortcomings of a conventional SMS network, an exemplary conventional SMS network will now be described in detail. Although the following example is described using terms and protocols mainly as defined by the North American standard IS-41, it will be apparent to one skilled in the art that the example is applicable to any networks that offer store-and-forward type short message service.
FIG. 5 shows an exemplary structure of a SMS network 500. The SMS network 500 typically includes one short message service center (SMSC) 501. The SMSC 501 typically includes a storage subsystem to store short messages that had failed to be delivered. The SMSC 501 typically further includes various interfaces (not shown) to receive short messages originating from various sources and protocols, such as a Voice Mail System (VMS) 508, paging networks using, e.g., Telocator Numeric Paging Protocol (TNPP) 509, devices using the Short Message Peer-to-Peer (SMPP) protocol 510 via TCP/IP, e-mail systems using the Simple Mail Transport Protocol (SMTP) 511, and/or devices using the Telocator Alphanumeric Protocol (TAP) 512. Some of the various sources of the short messages may be gateways to other networks.
The SMSC 501 may further include a gateway/interworking block (not shown) that enables the SMSC 501 to communicate with the rest of the SMS network 500, such as a Home Location Register (HLR) 503 or a Mobile Switching Center (MSC) 505, using the Signaling System No. 7 (SS7) 502. The methods and mechanism of communication in the SMS network 500 are defined by the mobile application part (MAP) layer, which uses the services of the SS7 transaction capabilities application part (TCAP) as the signaling infrastructure of the SMS network 500. The protocol for the signaling is referred to as the IS-41 protocol under the American standard as published by the Telecommunication Industry Association (TIA) or as the GSM MAP under the European standard published by European Telecommunication Standards Institute (ETSI).
The Home Location Register (HLR) 503 includes a database that permanently stores and manages subscriptions and service profiles of users having a subscription to the SMS network 500. Although only one HLR 503 is shown, the SMS network 500 may include two or more HLRs. The SMS network 500 also typically includes several visitor location registers (VLR) 504. A VLR 504 is a database temporarily holding information about visiting subscribers who move into its service area. Thus, a VLR 504 contains information regarding routing information for all subscribers within its service area, and informs the relevant HLR 503 of the availability and routing information regarding its subscribers. The mobile switching center (MSC) 505 obtains subscriber information from the VLR 504 to service visiting subscribers.
The mobile switching center (MSC) 505 performs switching and call control functions, and receives short messages from the SMSC 501 for delivery to the appropriate mobile subscriber 507 (shown, e.g., as a cellular phone handset). It is to be understood that, although only one MSC 505 is shown, the wireless network 500 may include two or more MSCs. The base station subsystem (BSS) 506 handles the wireless communications, e.g., RF transmission and reception of voice and data traffic, to and from the mobile subscriber 507. The BSS 506 is typically composed mainly of two parts: the base transceiver station (BTS, not shown) which houses the radio transceivers that define a cell and handles the radio-link protocols with the mobile subscriber 507, and the base station controller (BSC, also not shown) which manages the radio resources, and handles radio channel set up, frequency hopping, and handoffs (or handovers as is sometimes referred as). The BSC is the interface between the MSC 505 and the subscriber 507. The subscriber 507, also sometimes referred to as a mobile station (MS), typically consists of mobile equipment (e.g., a cellular phone handset) preferably uniquely identifiable by an identifying number, e.g., mobile identification number (MIN), International mobile subscriber identification (IMSI) and/or electronic serial number (ESN), for the subscriber 507. The mobile equipment may include a storage area, e.g., a flash memory, a ROM, a RAM or the like to hold the unique identifying number within the mobile equipment. In GSM networks, a smart card, typically referred to as a subscriber identity module (SIM) is utilized to store a unique identifying number.
FIG. 6 shows an exemplary flow of a short message through a conventional SMS network. Although FIG. 6 shows only an example of short message delivery to a mobile subscriber, it is to be understood that a mobile subscriber or any other sources may originate a short message. The flow of a mobile subscriber originated short message would involve similar processes as the following mobile subscriber terminated short message example, and would be apparent to one of ordinary skill in the art.
The SMSC 601 receives a short message intended for a subscriber 604 from a source of short message 605 which may be any one or more of the aforementioned sources of short messages, e.g., 508-512 of FIG. 5. Upon receiving a short message, the SMSC 601 sends a request for routing information, i.e., an SMS request (SMSREQ), to the HLR 602. The HLR 602 maintains information regarding the availability of the intended subscriber 604 and the appropriate MSC 603 that services the intended subscriber, and sends the information as routing information 608 back to the SMSC 601. The SMSC 601 forwards the short message to the appropriate MSC 603 using the routing information 608 received from the HLR 602, for example, in accordance with the short message delivery point-to-point (SMDPP) mechanism of IS-41 standard. The MSC 603 queries the VLR (not shown) for subscriber information. The VLR may perform a paging and authentication process, and sends the subscriber information to the MSC 603. The MSC 603, using the information received from the VLR, delivers the short message to the intended subscriber 604, and sends a delivery report 612 to the SMSC 601. The SMSC 601 may send the result of the delivery, i.e., the status report 613, to the source of the short message 605 if requested.
When the attempted delivery of the short message has failed because, for instance, the intended user was out of the service area, or had his or her communication device turned off, the MSC 603 informs the HLR 602 of the failure. The HLR 602 then turns on an SMS notification indicator flag for the subscriber, and the SMSC 601 retains the failed message for a later delivery attempt.
FIG. 7 shows a pending short message delivery process in a conventional short message service network after the mobile subscriber becomes available for delivery of the retained messages. In particular, in FIG. 7, when the subscriber 704 turns his or her handset on or comes within the service area, the subscribers handset sends a registration signal 709 to the MSC 703. The registration signal 709 may or may not include authentication process.
Upon receiving the registration signal 709, the MSC 703 informs the HLR 702 (or the VLR 711) of the availability of the subscriber 704 by sending a subscriber available signal 708. Because the SMS notification flag for the subscriber is on, the HLR 702 or the VLR 703 sends an SMS notification (SMSNOT) message 705 in case of networks implementing IS-41 standard, or an equivalent notification alerting the fact that the subscriber has become available in networks implemented in accordance with other standards, to the SMSC 701 assigned to service that particular intended subscriber 704.
The SMSC 701 then sends a delivery request 706 to the MSC 703 via, for example, the SMDPP protocol in the IS-41 standard. The MSC 703 finally delivers the short message 710 to the subscriber 704, and sends a message delivered message 707 back to the SMSC 701 to confirm and finalize the delivery of the short message. The SMSC 701 may further send a delivery report to the source of the short message if it was requested.
As can be appreciated, the conventional SMS networks are implemented with only one SMSC in the network servicing any particular subscriber and thus provides the HLR 702 without the ability to alert more than one SMSC of the fact that the subscriber has become available. Thus, a particular subscriber is limited to having only one short message delivery channel, typically from a single provider.
More recently, systems have been developed that attempt to employ more than one SMSC assigned to a particular subscriber, and thus attempt to provide multiple short message delivery channels. However, these attempted systems require extensive modifications to the conventional SMS network, adding unnecessary complexity, incompatibility with an otherwise conventional SMS network, and typically require service outage to subscribers while additional short message channels are being added.
In particular, U.S Pat. Nos. 5,682,600 ("the '600 patent") and 5,787,357 ("the '357 patent"), both to Salin, describe known SMS networks having more than one SMSC. Both patents propose the use of a list (kept by the system, e.g., by the HLR) of addresses of SMSCs that have tried and failed to deliver short messages intended for a particular subscriber who is unavailable to receive the messages at the time. When the subscriber becomes available, the system notifies all such SMSCs on the list.
However, as described by the '600 patent and the '357 patent, when there is more than one SMSC retaining short messages intended for the same subscriber, each SMSC will try, nearly simultaneously to each other, to initiate the forwarding of respective short messages to the subscriber upon being notified of the availability of the subscriber. Because only one short message can be transmitted to a subscriber at any one time, a short message collision occurs causing the receipt of negative acknowledgements prompting further storing of the rejected short messages in their respective SMSCs for a later attempted delivery. The situation will continue as long as there are more than one SMSC attempting to send a short message to the same subscriber, and has the potential of delaying delivery of even the initial short message to the intended subscriber. These exchanges of repeated unsuccessful attempts and the negative acknowledgements can result in a significant amount of extra traffic that may tend to waste available bandwidth of the network. Moreover, this problem becomes exacerbated if the subscriber had been unavailable for a long period of time and/or the subscriber received messages from many different sources during his absence, both of which tends to cause the stored buildup of large number of short messages.
To cure the problem after the first collision (and delay) has occurred, the '600 patent and the '357 patent propose a delay mechanism in the system to add delays between notifications to each of the SMSCs to avoid a simultaneous transmission of messages by multiple SMSCs. The short messages are stored in the system queue and forwarded one short message at a time by monitoring the respective completion of delivery of each short message.
The '600 patent requires the home location register (HLR) of the system to keep track of the addresses of SMSCs with failed message deliveries, and added delays between the notifications to the SMSCs, both of which result in added complexity to a conventional HLR.
The '357 patent requires a list kept in the HLR, added memory to the mobile switching center (MSC) memories to store and queue the short messages, and a mechanism to monitor the delivery process, e.g., to detect the completion of delivery of one short message in order to start the delivery of the next short message. Thus, '357 patent also adds significant complexity and cost to a conventional SMS network.
Moreover, both the solutions proposed by the '600 patent and the '357 patent require the SMS network to create and maintain a list of addresses of SMSCs, and to determine which and when SMSCs are to be notified, based on the list. This adds a source of error that may result in a wrong SMSC receiving the notification, resulting in failure of pending message delivery.
Moreover, and very importantly, the '357 and '600 patents require extensive communication and monitoring of SMSCs, which are often manuafactured by different companies at different times, and may therefore be quite incompatible with one another.
The added complexity of the network must also be provided for by the appropriate standards and/or protocols in order for the system to be seamlessly compatible with other networks.
Furthermore, SMS networks such as those described in the '600 and '357 patents are difficult to upgrade, expand and/or reconfigure, i.e., by adding more SMSCs, without significantly affecting the remaining portions of the SMS network, i.e., requiring significant modifications to the HLR and/or the MSC.
There is thus a need for an architecture and method for a SMS network that allows inclusion of multiple SMSCs without requiring significant and complex modification to the remaining SMS network elements, that can be easily upgraded, expanded and/or reconfigured, and that does not require the error prone creation of and selection from a list of addresses of SMSCs. Thus, there is a need for a more reliable and robust method and apparatus for delivering pending short messages to a subscriber from a plurality of SMSCs.